Alternating current solenoids

ABSTRACT

A solenoid construction for use as a flow control valve having a coil, and an armature in the form of a valve plunger which is disposed in a housing which forms a fluid barrier between the coil and plunger, and is formed of magnetic material to provide a flux path of low reluctance linking the coil with the immersed valve plunger.

UnitedtStates Patent Lang Mar. 7, 1972 [54] ALTERNATING CURRENTSOLENOIDS 2,613,439 97?)?5 G iiugi-Qlf "I. $251738 2,853,659 9/1958Herion .335 262 [72] gm' zhg 295 suffield 3,166,692 1/1965 Forrester etal. .335/251 [22] Filed: June 4, 1969 Primary Examiner-Amold Rosenthal[21] Appl. No.: 830,342 [57] ABSTRACT A solenoid construction for use asa flow control valve having [52] [1.8. CI ..25l/ 129, 251/141,3332;542:642, a coil and an armature in the form ofa valve plunger whichis 511 1111. c1. ..Fl6k 31/06, om/13 in a "wing which a fluid barrierbefween 58 Field or Search ..251/129, 141; 335/260, 262, coil andPlunger, and is firmed mmefic 2 33 5 /244 245 vide a flux path of lowreluctance linking the coil with the 1mmersed valve plunger. [56]References Cited 9 Claims, 3 on g UNITED STATES PATENTS unmet. .1.. .M.1

98?,9l8 4 12 1 1 .1 r r 1 srr6m .335/244 PATENTEDHAR 7 m2 SHEET 2 [IF 2FIG.2

FIGIS INVENTOR. GREGOR L. LANG ALTERNATING CURRENT SOLENOIDS BACKGROUNDThis invention relates to alternating current electromagnets useful insolenoid devices such as relays, actuators, and particularly in magneticfluid control valves of the type used to control the flow of gases orliquids under pressure in a closed system.

- In the design of solenoid fluid control valves it has been thepractice to provide a cylindrical plunger guide or cap member ofnonmagnetic material to serve as a housing for the movable valve plungerand a return biasing spring. The housing with appropriate gasketedassembly to the valve body, confines within. the cup whatever fluid iscontrolled by the valve. Such constructions are often referred to as wetarmature" valves. The exciting coil is provided with a magnetic shelland cylindrical pole members, designed to conduct the flux to thevicinity of the plunger housing with a minimum of gaps or magneticdiscontinuities, to thereby attain a relatively high magneticefficiency. The coil is commonly assembled about the housing, such thatwhen energized, the magnetic flux path is through the wall of thenonmagnetic housing and the plunger-armature. U.S. Pat. Nos. 2,627,544and 2,936,790 illustrate typical examples of solenoid valves constructedas described.

Because of the nonmagnetic cup between the plunger and the pole members,a truly closed magnetic circuit is not possible of attainment. The wall,thickness of the cup forms a gap across which. the flux must pass twice,on entering and leaving the armature. To be capable of withstanding thefluid or hydraulic forces encountered, it is necessary that the plungercup be of appreciable wall thickness, a typical value for a brass orbronze housing being 0.026 inch for a fluid pressure of 125 p.s.i. Thewall thickness represents an equivalent gap of 0.052 inch in anotherwise closed magnetic circuit. The presence of such a substantialgap in a closed AC magnetic circuit has the two fold effect of causingsharp reductions in inductive reactance, and in total flux flowing inthe system. Thus for a given applied voltage, a high current will flowin the solenoid, coupled with a material weakening in the mechanicalpull force attained by the armature. A result of these combined effectsis to cause electromagnets so constructed to operate at relatively highlevels of input wattage, and to therefore require in the solenoid, arelatively large number of costly copper windings for a given value ofmechanical force exerted by the armature. High input wattage and rapidtemperature rise have commonly been accepted as unavoidable incidencesof wet armature valve constructions heretofore available.

Past efforts to overcome those limitations have included the use ofhigh-strength nonmagnetic materials such as 18-8 stainless steel forthinner housing wall constructions, and also at a considerablemanufacturing cost, the use of immersed magnetic poles provided withannular shading rings. But these approaches yielded only slightimprovements in magnetic efficrency.

THE PRESENT INVENTION In accordance with this invention it has beenfound that in fluid control valves of the type described above, the cupor guide housing the armature may be constructed of thin ferromagneticmaterial such as A.I.S.I. type 430 stainless steel, chosen from thegroup known as straight chrome ferritic. Using this type of material,armature housings can be constructed with thin wall sections of adequatestrength to withstand the fluid pressures encountered in such valves.Moreover, the use of a magnetic material has the effect of essentiallyeliminating the magnetic gap invariably encountered in previous wetarmature valves. As a result, there is obtained a large increase intotal flux and in flux linking the armature, as well as in the value ofinductive reactance of the solenoid. The consequent decrease in currentvalue, input wattage, and temperature rise enable significant savings inthe weight, size, and cost of the copper winding required for a givenmechanical force exerted by the armature.

It is accordingly an important object of the present invention toprovide for a fluid control valve of the immersed armature type, asolenoid construction having an essentially gapless" or closed magnetic.circuit with resulting improvement, at reduced cost, in electromagneticefliciency and mechanical force attained by the armature, for a givenelectrical input.

Another object is to provide for a. magnetic fluid valve of the abovetype, a construction wherein for a. given fluid load on the annature,the required electrical power is reduced whereby the amount of copper inthe solenoid winding can be greatly reduced.

A further object is to provide for a magnetic fluid valve of the abovetype, a solenoid and magnetic circuit construction of such new and novelcharacter that the required electrical input power per unit of fluidpressure or fluid flow is decreased, whereby the heat dissipation andtime rate of temperature rise of said solenoid is reduced over-priorconstructions.

Another object is to provide for a magnetic fluid valve of the immersedarmature type, a solenoid and magnetic circuit of new and novelcharacter enabling increased armature forces, and increased fluid loads,pressures, and flowrates, for a given value of electrical input power.

A still further object is to provide for a magnetic fluid control valve,an armature housing constructed of ferromagnetic material having theproperty of hysteresis, to coact with a phase splitting core of the typedescribed in my copendingapplication Ser. No. 783,035, filed Dec. 1 l,1968, now U.S. Pat. No. 3,553,618. In this combination thephase-shifting effectiveness is further improved with resulting furtherimprovement of the solenoid magnetic efficiency.

Another important object is to provide an electromagnetic constructionof high efficiency for use in hermetically sealed devices commonly usedin vacuum or explosionproof systems wherein complete isolation by animpermeable barrier is requisite between the electrical energizing andmagnetically actuated elements of said devices.

An additional object is to provide a solenoid construction wherein ahousing or guide for the armature is constructed of ferromagneticmaterial, whereby'the distribution of'magnetic flux in and around saidarmature is controlled to yield an improved force-versus-distancecharacteristic, to thereby increase the wide gap pull value attained bysaid solenoid.

Yet another object is the provision in a flow control valve, of anarmature and a closely fitting magnetic housing which is characterizedby a motion-inhibiting piston or dashpot effect, serving to reduce thetendency of the valve to produce hydraulic noise or water hammereffects.

The foregoing and other objects and advantages of the invention willbecome apparent from the following description, and the accompanyingdrawings of a preferred embodiment, in which:

FIG. I is a cross-sectional view of a fluid valve embodying a solenoidaccording to this invention; and,

FIG. 2 is a sectioned partial view showing an alternative solenoidconstruction according to my copending application Ser. No. 783,035 forPhase Splitting Core, in combination herewith.

FIG. 3 is an enlarged partially sectioned view of the assembly of themagnetic core of FIG. 2.

Wet armature valve constructions heretofore available were presumablybased on the premise that the use of magnetic material as anarmature-plunger housing would act adversely as a magnetic shunt,bypassing a large portion of the available flux, thus reducing thetractive force exerted by the plunger.

The basis of this invention is my discovery that a valve solenoid havingan armature housing constructed of ferromagnetic material of relativelythin wall section, behaves in an unexpectedly opposite manner to thatpreviously postulated. The pulling force per unit of input power isgreatly in excess of the values obtained with the use of nonmagneticmaterial in said housing.

This apparently anomalous behavior is explained; first by the virtualelimination of the dual magnetic gaps, with a major increase in fluxflowing in the magnetic circuit due to the decrease in the reluctancethereof; and secondly by the fact that pole-to-pole shunting of flux bythe housing wall has a limited adverse effect because the thinferromagnetic housing wall becomes saturated at relatively low values offlux. As a result of the above saturation effect, the balance of theavailable flux comprising the greater part thereof, therefore flowsthrough the best alternate magnetic path which in the present case isrepresented by the plunger-armature, as will be hereafter described. Ithas been discovered that the relatively small loss of flux due toparallel shunting by the housing wall is more than compensated by thelarge increase in total magnetic circuit flux due to the above-mentionedelimination of the housing wall gaps. The resulting tradeoff yields asubstantial net gain in armature force available per unit of electricalinput power. I have observed gains in excess of I percent during testsof the present invention.

The combination of an armature and a closely fitted ferromagnetichousing yields a further benefit whereby the armature stroke vs. forcecharacteristic is modified in a manner favoring the initial, or wide gappull value, which I have found to be a desirable characteristic in fluidvalve usage, and in some other applications. This effect is believedexplainable as a modification of flux distribution in and around thearmature by the close proximity of my ferromagnetic housing, with saidflux distribution varying progressively as the armature moves from theinitial or open gap position, to the sealed, or closed gap position.

It will be apparent to those skilled in the art that many changes may bemade in the arrangement of parts and details of construction of thesolenoid devices described herein without departing from the spirit ofthe invention. Moreover, it will be understood that the applicationsshown as applied to fluid control valves are by way of illustrationonly, and that the several advantages of the invention are applicable toother tractive solenoid devices such as relays and clutches, as well asto hermetically sealed and explosionproof magnetic devices.

Referring more particularly to the drawings wherein similar referencecharacters designate corresponding parts throughout the various views;FIG. 1 is a median sectional view of a solenoid flow control valveaccording to the present invention in which cylindrical armature 1, andbias spring 2, are enclosed by armature housing 3, said housing beingconstructed of ferromagnetic material, and so dimensioned as to permitfree axially slidable motion therein by plunger-armature l. Armature lis formed with a projecting valve stem portion 4, having atits lower endan integrally formed conical valve portion designed to enter and sealfluid orifice 6 under the influence of bias spring 2, when the valve isdeenergized or closed. Bias spring 2 is of the conical compression typehaving its large diameter upper end supported by annular shoulderportion 11 formed in housing member 3, and having its small diameter endengaged with valve stem 4 by snapring 7, or other suitable means.Compression spring 2 thus biases armature 1 in a downward direction suchas to seal fluid orifice 6 when the valve is deenergized. When so biasedthe upper surface of armature l is separated from the inner abuttingsurface of magnetic cup 3, thus forming working gap 8 which allowsupward motion of armature 1, when the solenoid is energized.

Valve body 9 is formed of plastic or metal, and is provided with inletpipefitting l4, and outlet fitting 22, which are connected by integrallyformed fluid passages with the appropriate sides of the valve means.Inlet 14 is provided with an annular recess 16, adapted to receive wiremesh inlet strainer 15 which serves to prevent fluid-home particulatematter from entering the valve. Inlet 14 is connected by fluid duct 17to annular fluid channel 18, whereby the incoming fluid is conducted tothepressure chamber formed by the inside of the conical portion 12 ofplunger housing 3. The peripheral flange portion 13. of housing 3 ispressed into sealing contact with elastic sealing ring 20, by thedownward force exerted on annular pressure plate 19, by a number ofappropriately spaced assembly screws, not shown. Fluid seal ring 20,formed of an elastomer is seated in annular channel 21 formed in valvebody 9. Elastic ring 20 thus forms a compressibly deformed seal whichconfines the pressurized incoming fluid to the inside of said conicalpressure chamber.

Outlet fitting 22 is formed by a downward projecting portion of valvebody 9, generally tubular in form, and positioned coaxial with armatureplunger 1. Outlet fluid duct 23 extends upward to connect with fluidpassage 24 which passes vertically through annular valve seat member 25.Valve member 25 is molded of elastomeric material and is dimensioned tofit snugly inannular recess 26 formed in valve body 9, coaxial withfluid duct 23, and forming the upper extremity thereof. Fluid orifice 6forms the valve seat proper, being normally sealed by the engagementthereagainst of valve cone 5, when the solenoid is deenergized. Fluidpassage 24 forms a flow limiting restriction, the diameter beingappropriate to the fluid pressure, viscosity, and flow rate desired.

The magnetic solenoid is assembled over the cylinder cup portion ofhousing 3, coaxial therewith. The solenoid is comprised of copperwinding 27, on insulating spool 28, and is connected to the externalpower source by terminals or leads 29. The winding encloses soft ironcore piece 30, and is enclosed by mild steel magnetic outer shell 31, towhich pole piece 30 is attached at top center 32. Magnetic shell 31 hasin its lower surface a bore or hole dimensioned to fit snugly over thecylindrical cup portion of housing 3 which extends into winding spool 28to abut the lower end of core piece 30, thus completing the magneticcircuit linking solenoid 27 in an effectively closed manner. Adimensional length of core 30 equal to 75 percent of the length ofsolenoid winding 27 has yielded good results in tests.

FIG. 1 depicts the valve in deenergized state, with armature l in thedownward position thus forming axial gap 8 separating armature 1 fromthe diaphragm portion 33 of housing 3. Upon energization, themagnetomotive force deriving from the current flowing in solenoid 27gives rise to a concentration of flux flowing axially in the thincylindrical wall of housing 3, with a resulting saturation of the wall.The excess of available flux lines beyond the saturation level is thusdiverted radially through the wall of housing 3, thence axially througharmature 1, across gap 8 and through diaphragm 33 to core 30, thusdeveloping a pulling force which raises armature 1, compressing spring2, and opening passage 24 to allow the flow of fluid therethrough.

It can be noted that the upward travelof armature 1 causes working gap 8to vanish, with the previous gap space then becoming occupied by theupper portion of armature 1, thus completing a low-reluctance link inthe solenoid magnetic circuit, of relatively large cross section and lowsusceptibility to saturation. As a result there occurs a redistributionof flux whereby the greater part of the total flux will pass througharmature 1, with a minor portion of the flux flowing in the wall ofhousing 3 due to its small cross secton. A preponderance of theavailable flux will thus flow in armature 1 under both the open gap andclosed gap conditions.

It is therefore postulated that the housing wall operates in twodifi'ering and sequential magnetic states, varied by the motion orposition of armature 1. The housing wall becomes saturated by the highinrush current at energization, followed by a transition into a lesssaturated state as armature 1 reaches the full stroke or zero gapposition, with coil current dropping to the lower steady-state value.Both states result in the transfer of major values of flux into andthrough armature 1, thereby causing said armature to develop usefulvalues of mechanical pulling force.

The arrangement of armature 1 with a closely fitted housing 3, asdisclosed in FIG. 1 provides further functional benefits resulting froman inherent dashpot orfluid damping effect. Said damping effect servesto reduce the tendency of an AC solenoid to produce intermittent pullforces and buzzing sounds, when phase-splitting means are not employed,as in FIG. 1 where core piece is of the simple cylindrical type. Thediametral clearance between armature 1 and housing 3 may be varied tocontrol the damping and rate of movement of armature l, as thecontrolled fluid enters and leaves gap area 8. The force and rate ofbias spring 2 becomes an important design factor, since spring forcetogether with the above armature diametral clearance, are basic indetermining the rate at which armature 1 moves downward afterdeenergization of solenoid 27. The above damping effect may be furthermodified for fluids of varying viscosity by providing an axially alignedfluid passage through armature l, or by providing axially alignedleakage grooves in the periphery of said armature. The fluid dampingserves beneficially to reduce the tendency of the valve to producehydraulic-hammer and other fluid surge or transient effects arising fromrapid armature motion.

FIG. 2 depicts a solenoid construction in which a phase splitting coreof a self-shading type described in my copending patent application Ser.No. 783,035 is used in lieu of the plain cylindrical core 30 of FIG. 1,yielding a further major improvement in magnetic efficiency and pullforce, over the values obtainable with said cylindrical iron core. Thesolenoid construction of FIG. 2 is directly usable with the valveconstruction of FIG. 1, the related valve description thus beingapplicable to FIG. 2.

The twopiece annular core 34 and 35 makes use of the discovered factthat hysteresis and eddy currents in flux carrying core members may beeconomically and efficiently used to obtain phase retardation andresultant phase splitting in AC devices in lieu of shading ringspreviously used for that purpose. The core assembly including soft ironouter sleeve 34, and mild steel inner cylindrical member 35, is shown insection in FIG. 2, and also in an enlarged partially sectioned view inFIG. 3 which discloses the annular and peripheral gap means whichcontribute to the phase splitting function and high magnetic efficiencyof said core assembly.

Outer cylindrical core member 34 is the leading phase flux path, beingdesigned to introduce a minimum of phase retardation of the flux waveflowing therein. To that end it is constructed of a low hysteresismaterial such as silicon steel of annealed ingot iron. It is furtherprovided with a longitudinal slot 36, which extends the full length ofsaid sleeve thus interrupting the phase retarding circumferentialcirculating current which would otherwise flow therein. The flux waveflowing in sleeve 34 is thus substantially in phase with the alternatingmagnetomotive force established by the current flowing in exciting coil27.

Inner cylindrical core member 35 is the lagging phase or retardant fluxpath, being designed to obtain a substantial value of flux wave phaseretardation by the combined-effects of hysteresis and internalcirculating currents. Member 35 is constructed of a milk steel such ascold-rolled A.I.S.I. C-lll7 which is characterized by a moderate degreeof inherent hysteresis or remanence, such as to cause an effective phaseretardation of the flux wave flowing therethrough. Moreover, member 35is designed as an unbroken cylindrical body which is subject to the flowof circular induced eddy currents throughout its length. Said eddycurrents serve to oppose changes in the instantaneous flux value flowingin said member, thus retarding the phase of the resultant flux wave, inaddition to the hysteretic phase retardation aforesaid. The resultantangular phase shift is thus a composite value which may be considered asthe vector sum of the two phase lag angles obtained separately from theretarding effects of magnetic hysteresisand eddy current flow.

An annular gap 37 provides for magnetic separation of the two coremembers 34 and 35, to avoid interphase shunting of fluxcomponentsdue tothe proximity of the two members. Gap'37 is indicated in FIG. 3,produced by forming member 35 with a step or shoulder 38 whereby thelower portion of core 35 is slightly smaller in diameter than the insideof sleeve 34. A satisfactory dimension for-said gap has been found to beprovided by forming shoulder 38 with a. radial dimension equal to 2%percent of the outside diameter of sleeve 34. The

axial length of gap 37 may be between 70 and percent of the length ofsleeve member 34. While the annular gap space 37 is shown in the drawingas an airgap, it will be apparent to those skilled in the art that thegap space may alternatively be filled with an appropriate nonmagneticmaterial such as plastic or cement, to maintain concentricity and secureadhesron.

In the absence of mathematical expressions reliable applicable to thepresent invention, an experimental test program was undertaken toprovide a basis for mathematical definition, and to establish optimum ornear-optimum dimensions, materials,

and size ratios for a water valve application similar to that shown inFIGS. 1 and 2. A flow rate of 1.0 g.p.m. was chosen, with operation on 115 v. 60-cycle AC with a water gauge pressure of 60 p.s.i. The diameterof fluid passage 24 was established as 0.072 inch, and an armaturetravel of 0.063 inch was chosen, thus setting the axial dimension ofworking gap 8 at 0.063 inch. An armature open-gap (inrush) pullrequirement of 10 oz. was established to allow a reserve over themaximum load values to be encountered.

The following dimensions and size ratios were established:

Coil spool 28, length o.a., 0.820 inch, winding length 0.760

inch.

Coil 27 3,900 turns, No. 39 or 40 B&S ga. copper, weight 8 or ll gm.

Core 30, 0.600 inch long, 0.437 inch dia., magnetic ingot tron.

Core sleeve 34, 0.600 inch long, 0.437.dia, 0.062 wall, ingot iron.

Core 35, 0.600 inch long, dias. 0.296 ,inch & 0.316 inch,

C-1 1 l7 c.r.s.

Housing 3, cup 0.437 inch o.d., 0.405 inch i.d., wall 0.016

inch, 430 8.8.

Armature 1, dia. 0.395 inch to 0.400 inch,,plunger length 0.325 inch,430 8.8.

Magnetic shell 31, 12 ga. X 0.812 inch w. l,0l2-h.r.s. Butt at topcenter.

For evaluation purposes a numerical performance .factor of merit P wasdevised as an expression of open gap pull in ounces attainable, per wattof steady state electrical. input. For the present examples -P" becomes10 (oz.),divided-by the measured input watts (w.) for the closed gapsteady-state condition. A commercial prior art water valve of similarcapacity was included in the test series as a comparison base, with thesupply voltage adjusted to obtain 10 Oz. of armature pull .at inrush. Atthat voltage it consumed 16 watts, steady state, for a value P=0.625.

Values obtained for the present invention were:

Assembly of FIG. 2

with nonmagnetic housing 3, Assembly of FIG. 1,

with magnetic housing 3, Assembly of FIG. 2,

with magnetic housing 3,

In the combination construction of FIG. 2, I have observed that the useof hysteretic material in the construction of housing 3 adds further tothe pull values obtainable. This result presumably arises from acooperative phase shifting effect whereby the hysteretic property ofhousing 3 adds to the angular phase shift produced by core assembly 34,and 35.

The use in this invention-of hysteretic materials-has ,been found not tocause. undue difficulties with "sticking armature" due to remanence orresidual flux. Although annealing of outer shell.3l after forming ,isdesirable, attention to the force and rate of spring 2, has providedfreedom from residual flux problems. It thus appears that housing 3servesbeneficially as a saturable magneticshunt, bypassing aroundarmature l a portion of the residual flux originating in parts such ascore 30, shell 31, or core 35. The bypassing of residual flux iseffective up to the saturationlevel of the cylindrical wall of housing3, thus representing a further benefit accruing to the presentinvention.

From the foregoing it will be apparent that I have provided novel,simple, and economical means of attaining the objects and advantagesrecited.

Having described my invention, 1 claim:

1. In a magnetomotive device having a coil with a core and an armaturearranged to form a magnetic circuit, a housing for said armature, saidcore including a composite flux conducting element comprising aplurality of ferromagnetic portions defining spaced magneticallyparallel flux paths, said portions incorporating relative variations inat least one of the electromagnetic properties thereof includingmagnetic hysteresis and eddy current susceptibility, said portions beingin fixed relative position and being magnetically separated over asubstantial portion of their common length by substantially nonmagneticgap means extending therebetween.

2. A magnetomotive device as set forth in claim 1 in which said housingis a fluid confining barrier interposed between said armature and saidcoil.

3. In a magnetomotive device having a coil with a core and an armaturearranged to form a flux path, a substantially closed magnetic circuitincluding a tubular housing for said armature, said housing being ofunitary construction having one and closed by a transverse diaphragmportion, said housing including said diaphragm portion being formedthroughout of ferromagnetic material providing an uninterrupted fluxpath throughout the tubular wall and diaphragm portions thereof and inwhich at least the tubular wall portion thereof is substantially thesame thickness throughout its entire length.

4. A magnetomotive device as set in claim 3 in which said housing is afluid confining barrier interposed between said armature and said coil.

5. A magnetomotive device as set forth in claim 3 in which said housingis arranged as a fluid confining element of an associated fluid controlvalve, said armature being immersed in the fluid controlled by saidvalve.

6. In a magnetomotive device having a coil with a core and an armaturearranged to form a magnetic circuit, a housing for said armature, saidcore including a composite flux conducting element comprising aplurality of ferromagnetic portions defining spaced magneticallyparallel flux paths, said portions incorporating relative variations inat least one of the electromagnetic properties thereof includingmagnetic hysteresis and eddy-current susceptibility, said portions beingmagnetically separated over a substantial portion of their common lengthby substantially nonmagnetic gap means extending therebetween, saidportions including an inner cylindrical member and an outer sleevemember arranged in an annular coaxial manner, said sleeve member havingits circumferential electrical continuity substantially interrupted.

7. ln a magnetomotive device having a coil with a core and an armaturearranged to form a magnetic circuit, a housing for said armaturearranged as a fluid confining element of an associated fluid controlvalve, said core including a composite flux conducting elementcomprising a plurality of ferromagnetic portions defining spacedmagnetically parallel flux paths, said portions incorporating relativevariations in at least one of the electromagnetic properties thereofincluding magnetic hysteresis and eddy current susceptibility, saidportions being magnetically separated over a substantial portion oftheir common length by substantially nonmagnetic gap means extendingtherebetween, said armature being immersed in the fluid controlled bysaid valve.

8. In a magnetomotive device having a coil with a core and an armaturearranged to form a magnetic circuit, a housing for said armature, saidcore including a composite flux conducting element comprising aplurality of ferromagnetic portions defining spaced magneticallyparallel flux paths, said portions incorporating relative variations inat least one of the electromagnetic properties thereof includingmagnetic hysteresis and eddy current susceptibility, said portions beingmagnetically separated over a substantial portion of their common lengthby substantially nonmagnetic gap means extending therebetween, saidhousing being of tubular form and of integral construction having oneend closed by a transverse diaphragm portion, said housing being fonnedof ferromagnetic material of substantially uniform thickness, said coreand said armature forming a substantially closed flux path includingsaid housing.

9. In a magnetic fluid valve having a coil with a core and an armaturearranged to form a flux path, a substantially closed magnetic circuitincluding a tubular housing for said armature, said housing being ofintegral construction having one end closed by a transverse diaphragmportion, said housing being formed of ferromagnetic material ofsubstantially uniform thickness, said armature being disposed withinsaid housing for operative movement and having fluid valving means inoperative association therewith, said core including a composite fluxconducting element comprising a plurality of ferromagnetic portionsdefining spaced magnetically parallel flux paths, said portionsincorporating relative variations in at least one of the magneticproperties thereof including magnetic hysteresis and eddy currentsusceptibility, said portions being magnetically separated over asubstantial portion of their common length by substantially nonmagneticgap means extending therebetween.

l t l

1. In a magnetomotive device having a coil with a core and an armaturearranged to form a magnetic circuit, a housing for said armature, saidcore including a composite flux conducting element comprising aplurality of ferromagnetic portions defining spaced magneticallyparallel flux paths, said portions incorporating relative variations inat least one of the electromagnetic properties thereof includingmagnetic hysteresis and eddy current susceptibility, said portions beingin fixed relative position and being magnetically separated over asubstantial portion of their common length by substantially nonmagneticgap means extending therebetween.
 2. A magnetomotive device as set forthin claim 1 in which said housing is a fluid confining barrier interposedbetween said armature and said coil.
 3. In a magnetomotive device havinga coil with a core and an armature arranged to form a flux path, asubstantially closed magnetic circuit including a tubular housing forsaid armature, said housing being of unitary construction having one andclosed by a transverse diaphragm portion, said housing including saiddiaphragm portion being formed throughout of ferromagnetic materialproviding an uninterrupted flux path throughout the tubular wall anddiaphragm portions thereof and in which at least the tubular wallportion thereof is substantially the same thickness throughout itsentire length.
 4. A magnetomotive device as set in claim 3 in which saidhousing is a fluid confining barrier interposed between said armatureand said coil.
 5. A magnetomotive device as set forth in claim 3 inwhich said housing is arranged as a fluid confining element of anassociated fluid coNtrol valve, said armature being immersed in thefluid controlled by said valve.
 6. In a magnetomotive device having acoil with a core and an armature arranged to form a magnetic circuit, ahousing for said armature, said core including a composite fluxconducting element comprising a plurality of ferromagnetic portionsdefining spaced magnetically parallel flux paths, said portionsincorporating relative variations in at least one of the electromagneticproperties thereof including magnetic hysteresis and eddy-currentsusceptibility, said portions being magnetically separated over asubstantial portion of their common length by substantially nonmagneticgap means extending therebetween, said portions including an innercylindrical member and an outer sleeve member arranged in an annularcoaxial manner, said sleeve member having its circumferential electricalcontinuity substantially interrupted.
 7. In a magnetomotive devicehaving a coil with a core and an armature arranged to form a magneticcircuit, a housing for said armature arranged as a fluid confiningelement of an associated fluid control valve, said core including acomposite flux conducting element comprising a plurality offerromagnetic portions defining spaced magnetically parallel flux paths,said portions incorporating relative variations in at least one of theelectromagnetic properties thereof including magnetic hysteresis andeddy current susceptibility, said portions being magnetically separatedover a substantial portion of their common length by substantiallynonmagnetic gap means extending therebetween, said armature beingimmersed in the fluid controlled by said valve.
 8. In a magnetomotivedevice having a coil with a core and an armature arranged to form amagnetic circuit, a housing for said armature, said core including acomposite flux conducting element comprising a plurality offerromagnetic portions defining spaced magnetically parallel flux paths,said portions incorporating relative variations in at least one of theelectromagnetic properties thereof including magnetic hysteresis andeddy current susceptibility, said portions being magnetically separatedover a substantial portion of their common length by substantiallynonmagnetic gap means extending therebetween, said housing being oftubular form and of integral construction having one end closed by atransverse diaphragm portion, said housing being formed of ferromagneticmaterial of substantially uniform thickness, said core and said armatureforming a substantially closed flux path including said housing.
 9. In amagnetic fluid valve having a coil with a core and an armature arrangedto form a flux path, a substantially closed magnetic circuit including atubular housing for said armature, said housing being of integralconstruction having one end closed by a transverse diaphragm portion,said housing being formed of ferromagnetic material of substantiallyuniform thickness, said armature being disposed within said housing foroperative movement and having fluid valving means in operativeassociation therewith, said core including a composite flux conductingelement comprising a plurality of ferromagnetic portions defining spacedmagnetically parallel flux paths, said portions incorporating relativevariations in at least one of the magnetic properties thereof includingmagnetic hysteresis and eddy current susceptibility, said portions beingmagnetically separated over a substantial portion of their common lengthby substantially nonmagnetic gap means extending therebetween.